DE102008004247A1 - Piezoelectric actuator module - Google Patents

Abstract

A piezoelectric actuator module (19) for a fuel injection valve (1) has an actuator body (23) which has a plurality of ceramic layers (26, 27) and a plurality of electrode layers (28, 29) arranged between the ceramic layers (26, 27) ) having. In this case, the actuator body (23) is surrounded by a coating (40) which is formed by a sol-gel transformation.

Description

State of the art

The The invention relates to a piezoelectric actuator module for a fuel injection valve and a fuel injection valve with such a piezoelectric actuator module. Specially concerned the invention the field of injector for fuel injection systems of air-compressing, self-igniting internal combustion engines.

From the DE 102 17 361 A1 For example, a piezoelectric element and an injection nozzle provided with this piezoelectric element are known. The known piezoelectric element comprises a ceramic lamination, which alternately stacked one above the other contains a plurality of ceramic layers of piezoelectric ceramic and a plurality of internal electrode layers. On a part of the surface of the ceramic lamination, an organic insulating layer of organic material is formed. Further, an inorganic insulating layer of inorganic material is formed on the organic insulating layer. In this case, the organic insulating layer has enough elasticity to absorb the deflection of the piezoelectric element.

That from the DE 102 17 361 A1 known piezoelectric element and provided with this piezoelectric element injection nozzle have the disadvantage that the configuration is relatively complex. Further, there is the problem that openings or cracks in the inorganic insulating layer occurring during manufacture or operation allow fuel to penetrate into the organic insulating layer, causing short circuits between the inner electrode layers.

Disclosure of the invention

The Piezoelectric actuator module according to the invention the features of claim 1 and the invention Have fuel injection valve with the features of claim 10 the advantage of being a relatively inexpensive manufacture allowing, while providing reliable protection is guaranteed to the media, and that in particular a high reliability and functionality guaranteed is.

By the measures listed in the dependent claims are advantageous developments of specified in claim 1 piezoelectric actuator module and specified in claim 10 Fuel injection valve possible.

In Advantageously, the coating that is the actuator body surrounds, formed by a sol-gel transformation. The production of Coating can be carried out by a sol-gel process whose Special feature is that the production or deposition the materials each of a liquid sol state which transforms into a solid gel state by the sol-gel transfortmation becomes.

When Sols are called dispersions of solid particles, the particle size advantageously in the range of about 1 nm to about 100 nm can. The particles are preferably finely distributed, that is, dispersed, in water or organic solvents. A sol-gel process can advantageously be used by sol systems based on organometallic polymers. The transition from the liquid sol to the ceramic material takes place via a gel state. During the sol-gel transformation takes place preferably a three-dimensional crosslinking of the nanoparticles in the Solvent, whereby the gel has solid state properties receives. The transfer of the gel into one oxide ceramic material or the like takes place in an advantageous manner Way by a controlled heat treatment in air.

The initially liquid sol film can be inexpensively applied to an outer surface of the actuator body 23 are applied, wherein unevenness, in particular edges and depressions, filled and compensated by the sol film. The initially liquid sol film then transforms after a short drying in a solid gel film. This gel film can be subjected to a heat treatment under an oxygen-containing atmosphere, in particular air. For example, a decomposition of the organic constituents of the organometallic polymers can be achieved in a heat treatment up to about 400 ° C, wherein the organic components in the form of carbon dioxide and water escape. The remaining amorphous and nanoporous metal oxide film can be sintered at temperatures above 500 ° C, for example. At the same time, nucleation and crystal growth take place during the heat treatment, so that a crystalline, in particular nanocrystalline, dense, oxide-ceramic film is formed from the amorphous and porous gel film.

A sol-gel process is generally a wet-chemical process for producing ceramic or ceramic-organic materials. Such a general sol-gel process can be used for the production of ceramic bulk materials, ceramic nanopowders and fibers as well as for the deposition of homogeneous nanocrystalline oxide-ceramic or even ceramic-organic coatings. In the context of the invention, the sol-gel process for forming the coating which surrounds the actuator body is used. The coating is formed by a sol-gel transformation.

One Advantage of the design of the coating by a sol-gel transformation is that, where appropriate, a multi-layered Coating system completely by a coating, which is generated in the sol-gel process, can be replaced, so that a cost-effective production is possible. Furthermore, the properties of the coating in terms of be adjusted to a pressure and media resistance suitable. For example, a pressure and fuel resistant coating, which seals the actuator body can be generated.

In Advantageously, the coating is based on organometallic Polymers crosslinked by the sol-gel transformation formed. Furthermore, it is advantageous that the coating on the basis of dissolved in a solvent as nanoparticles organometallic polymers, wherein the nanoparticles through the sol-gel Transfortmation three-dimensional are crosslinked in the solvent is formed. there It is advantageous that the nanoparticles in the solvent a size from a range of about 1 nm to have about 100 nm. This can be a pressure and media resistant Coating can be achieved, which also designed relatively thin can be.

In Advantageously, an external electrode connection provided, which is surrounded by the coating. It can in the preparation of the coating of the present in the sol state Material after applying the sol-gel process a heat treatment process be subjected to pyrolysis, sintering and crystallization a coating in the form of one oxide ceramic, thin To train films. In this case, the external electrode connection is preferred designed as a heat-resistant electrode connection, to a sufficient temperature resistance, in particular during sintering, to ensure.

Brief description of the drawings

preferred Embodiments of the invention are in the following Description with reference to the accompanying drawings, in which corresponding elements with matching reference numerals are provided, explained in more detail. It shows:

1 a fuel injection valve with a piezoelectric actuator module in a schematic sectional view according to an embodiment of the invention;

2 a cut along in 1 Denoted by II section line through a piezoelectric actuator module according to the embodiment of the invention and

3 a process diagram for explaining the production of the piezoelectric actuator module of the fuel injection valve of the embodiment of the invention.

embodiments the invention

1 shows a fuel injector 1 with a piezoelectric actuator 2 according to a first embodiment of the invention. The fuel injector 1 can be used in particular as an injector for fuel injection systems of air-compressing, self-igniting internal combustion engines. A preferred use of the fuel injection valve 1 consists of a fuel injection system with a common rail, the diesel fuel under high pressure to several fuel injection valves 1 leads. The piezoelectric actuator according to the invention 2 is particularly suitable for such a fuel injector 1 and also for an inverse control of the piezoelectric actuator 2 , The fuel injection valve according to the invention 1 and the piezoelectric actuator according to the invention 2 However, they are also suitable for other applications.

The fuel injector 1 has a valve housing 3 and one with the valve body 3 connected fuel inlet nozzle 4 on. To the fuel inlet nozzle 4 a fuel line is connectable to the fuel injector 1 via a common rail or directly to a high-pressure pump. About the fuel inlet nozzle 4 can then fuel into one inside the valve body 3 provided actuator space 5 be initiated, so that in the operation of the fuel injection valve 1 Fuel in the actuator room 5 , in which also the piezoelectric actuator 2 is provided is located. The actuator room 5 is through a housing part 6 from one also inside the valve body 3 provided fuel space 7 separated. In the housing part 6 There are passage openings 8th . 9 designed to be over the fuel inlet 4 in the actuator room 5 led fuel into the fuel chamber 7 to lead.

The valve housing 3 is with a valve seat body 10 connected to which a valve seat surface 11 is trained. The valve seat area 11 acts with a valve closing body 12 to a sealing seat together. Here is the valve closing body 12 integral with a valve needle 15 formed, via which the valve closing body 12 with one in the actuator room 5 provided pressure plate 16 connected is. Here is the valve needle 15 through the housing part 6 along an axis 17 of the fuel injection valve 1 ge leads. A spring element 18 on the one hand on the housing part 6 and on the other hand on the printing plate 16 abuts applied to the piezoelectric actuator 2 with a biasing force, wherein by the addition of the valve needle 15 by means of the pressure plate 16 is actuated, so that between the valve closing body 12 and the valve seat surface 11 formed sealing seat is closed.

In addition, the valve housing has 3 a connection element 20 to connect an electrical lead to the fuel injector 1 to enable. The electrical lead can thereby by means of a plug to electrical lines 21 . 22 be connected. The electrical wires 21 . 22 are through the case 3 and one to an actuator body 23 of the actor 2 attached actuator foot 24 to the actuator body 23 guided. To the actuator body 23 of the piezoelectric actuator 2 is also an actuator head 25 attached, over which the actuator body 23 against the force of the spring element 18 on the printing plate 16 acts. The piezoelectric actuator 2 has the actuator body in the illustrated embodiment 23 , the actor foot 24 and the actuator head 25 on, leaving an actuator module 19 is formed.

The actuator module 19 can also consist of two or more actuator bodies 23 be constructed. In this case, between the individual actuator bodies 23 Be provided intermediate pieces or the individual actuator body 23 can also be glued together at their faces.

The actuator body 23 of the piezoelectric actuator 2 has a variety of ceramic layers 26 . 27 and a plurality of between the ceramic layers 26 . 27 arranged electrode layers 28 . 29 on. There are in the 1 to simplify the presentation of the ceramic layers 26 . 27 as well as the electrode layers 28 . 29 characterized. On an outer surface 35 of the actuator body 23 are external electrode connections 36 . 37 provided with the electrical wiring 21 . 22 are connected. The external electrode connections 36 . 37 are alternating with the electrode layers 28 . 29 connected so that alternating positive and negative electrodes between the ceramic layers 26 . 27 are provided.

Instead of the external electrode connections 36 . 37 it is also possible for internal electrode connections to be provided inside the actuator body 23 with the electrode layers 28 . 29 are contacted. Furthermore, it is also possible that an internal electrode connection with an external electrode connection 36 . 37 combined.

About the electrical wires 21 . 22 can the piezoelectric actuator 2 be charged, with this in the direction of the axis 17 expands so that the between the valve closing body 12 and the valve seat surface 11 trained sealing seat is opened. This leads to the spraying of fuel from the fuel chamber 7 over an annular gap 30 and the open sealing seat. When unloading the piezoelectric actuator 2 this contracts again so that the between the valve closing body 12 and the valve seat surface 11 trained sealing seat is closed again.

The actuator body 23 is on its outer surface 35 with a coating 40 surround. A part 41 the coating 40 extends to the actuator foot 24 and another part 42 the coating 40 also extends to the actuator head 25 , The coating is formed by a sol-gel transformation. This covers the coating 40 also the external electrode connections 36 . 37 on the outside surface 35 of the actuator body 23 are provided. Depending on the configuration of the external electrode connections 36 . 37 can the coating 40 the external electrode connections 36 . 37 also only partially cover, for example, if the external electrode connections 36 . 37 from the coating 40 led out.

The coating 40 is formed as a nanocrystalline, dense oxide-ceramic film, so that a pressure and fuel-resistant coating is given. The coating 40 thus forms in relation to that in the actuator room 5 provided under high pressure fuel a reliable seal against the actuator body 23 and optionally further elements of the piezoelectric actuator 2 , In particular, contact with the fuel or its constituents is prevented. In the case of a diesel fuel, for example, there is a risk that water contained in the diesel fuel to the actuator body 23 penetrates and a short circuit between the electrode layers 28 . 29 causing it to failure of the piezoelectric actuator 2 can come.

2 shows a section through the in 1 shown piezoelectric actuator 2 of the actuator module 19 of the fuel injection valve 1 along the section line marked II. The external electrode connections 36 . 37 are shown simplified and may for example have a woven structure. The actuator body 23 has rounded edges 42 . 43 . 44 . 45 on. Thus, sharp or sharp edges are avoided. This facilitates the application of the material for the coating 40 in the liquid sol state. However, in the area of the external electrode connections 36 . 37 in one area, for example 46 , Edges and a transition from the outer surface 35 of the actuator body 23 on the structure of the external electrode connection 37 given. The material for the coating 40 in the liquid sol state adapts to the conditions in the area 46 so that cavities or the like are filled up so that in the finished coating 40 Cavities prevented or at least reduced.

The production of the coating 40 is below based on the 3 further described in detail.

3 shows a process diagram for explaining the production of the piezoelectric actuator 2 of the piezoelectric actuator module 19 , It is specifically the production of the coating 40 that the actuator body 23 surrounds, explains. The process diagram explains the manufacture in relation to the steps 50 to 55 to which the following keywords are assigned:

50

"Begin of the process ";

51

"Sol production";

52

"Dip coating";

53

"Drying: Gel-film ";

54

"Heat treatment in air at about 300 ° C to about 800 ° C ";

54a

"About 300 ° C: pyrolysis ";

54b

"About 450 ° C: sintering and crystallization "and

55

"The End of the process: thin ceramic film ".

The process begins in step 50 , This is the still uncoated actuator body 23 before, on the possibly the external electrode connections 36 . 37 are attached.

In step 51 For example, there is a material in the liquid sol state, wherein the sol is a dispersion of solid particles in the size range of about 1 nm to 100 nm, which is finely dispersed, that is dispersed, in water or organic solvents.

In step 52 the material is in the liquid sol state on the outer surface 35 of the actuator body 23 deposited. The deposition can also affect the actuator body 23 and the actuator foot 24 extend to the actuator body 23 are attached. The deposition is carried out by dip coating, wherein the actuator body 23 at least partially immersed in the liquid sol and optionally moved, in particular rotated, is. The deposition in the step 52 However, it can also be done in other ways.

On the step 52 follows the step 53 in which the liquid sol is dried. In this case, a sol-gel transformation takes place, in which the deposited material is converted from a liquid sol state into a solid gel state. During the sol-gel transformation, three-dimensional crosslinking of the nanoparticles in the solvent occurs, giving the gel solid-state properties. The coating present in this state 40 is the geometry and contour of the actuator body 23 as well as the external electrode connections 36 . 37 customized.

In that on the step 53 following step 54 there is a transfer of the gel of the coating 40 in an oxide-ceramic material by controlled heat treatment under air. The heat treatment can also be carried out under a different atmosphere containing oxygen. In this embodiment, the step is 54 in two steps 54a . 54b divided up. In the first step 54a a pyrolysis is carried out. In this case, decompose the organic constituents of the organometallic polymers to about 400 ° C and escape in the form of carbon dioxide and water. The remaining amorphous and nanoporous metal oxide film is in the step 54b sintered at temperatures above 500 ° C. At the same time find in step 54b Nucleation and crystal growth take place, so that a crystalline, in particular nanocrystalline, dense, oxide-ceramic film is formed from the amorphous and porous gel film.

After the step 54 can the process with the step 55 be terminated, with the coating 40 in the form of a thin ceramic film. Depending on the application, the steps 52 . 53 and 54 also be repeated one or more times as indicated by the jump arrow 47 is illustrated. In this case, follow the step 54 the step 52 in which a further dip coating of the already partially coated actuator body 23 he follows. Thus, the thickness of the coating 40 be specifically influenced.

The Invention is not limited to the described embodiments limited.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 10217361 A1 [0002, 0003]

Claims (11)

Piezoelectric actuator module ( 19 ), in particular actuator module for fuel injection valves, with at least one actuator body ( 23 ) comprising a plurality of ceramic layers ( 26 . 27 ) and a plurality of between the ceramic layers ( 26 . 27 ) arranged electrode layers ( 28 . 29 ), characterized in that the actuator body ( 23 ) of a coating ( 40 ) and that the coating ( 40 ) is formed by a sol-gel transformation. Piezoelectric actuator module according to claim 1, characterized in that the coating ( 40 ) based on organometallic polymers crosslinked by the sol-gel transformation. Piezoelectric actuator module according to claim 2, characterized in that the coating ( 40 ) based on the dissolved in a solvent as nanoparticles organometallic polymers, wherein the nanoparticles are crosslinked by the sol-gel transformation three-dimensionally in the solvent is formed. Piezoelectric actuator module according to claim 3, characterized characterized in that the nanoparticles in the solvent a size from a range of about 1 nm to about 100 nm. Piezoelectric actuator module according to one of claims 1 to 4, characterized in that the coating ( 40 ) is designed as an oxide ceramic coating (409). Piezoelectric actuator module according to claim 5, characterized characterized in that the coating as nanocrystalline, denser, oxide ceramic film is formed. Piezoelectric actuator module according to one of claims 1 to 6, characterized in that at least one external electrode connection ( 36 . 37 ) provided on an outer surface ( 35 ) of the actuator body ( 23 ) is arranged, that the external electrode connection ( 36 . 37 ) of the coating ( 40 ), which the actuator body ( 23 ) is at least partially covered, that the external electrode connection ( 36 . 37 ) as a heat-resistant electrode connection ( 36 . 37 ) is executed and that on the with the external electrode connection ( 36 . 37 ) provided actuator body ( 23 ) applied coating ( 40 ) is subjected to a subsequent sol-gel transformation heat treatment. Piezoelectric actuator module according to claim 7, characterized in that the coating ( 40 ) a media-resistant coating ( 40 ). Piezoelectric actuator module according to claim 8, characterized in that the coating ( 40 ) a pressure- and fuel-resistant coating ( 40 ). Fuel Injector ( 1 ), in particular injector for fuel injection systems of air-compressing, self-igniting internal combustion engines, with a piezoelectric actuator module ( 19 ) according to one of claims 1 to 10 and one of the actuator module ( 19 ) operable valve closing body ( 12 ), which is provided with a valve seat surface ( 11 ) cooperates to a sealing seat. Fuel injection valve according to claim 10, characterized in that the piezoelectric actuator module ( 19 ) in an actuator room ( 5 ) and that the piezoelectric actuator module ( 19 ) in operation in the actuator room ( 5 ) is exposed under high pressure fuel.